Polybutylene terephthalate (PBT) reinforced with thermally stable reinforcing fibers such as glass fibers is well known as a molding resin and is described in numerous patents and publications including for instance U.S. Pat. No. 3,814,725. Fiber reinforcement generally improves the tensile strength, flexural strength, flexural modulus and heat deflection temperature of the molding composition. However, moldings, especially injection moldings of large fiber-reinforced articles of PBT, tend to display distortion or warping while some other resins of otherwise less desirable properties do not present such problems. It is believed that such warping is due to the presence of the very reinforcing fibers which contribute to the enhanced physical characteristics of the finished product.